Magnetic recording medium and magnetic storage apparatus

ABSTRACT

A magnetic recording medium is constructed to include a substrate, a magnetic layer made of a Co or Co-based alloy, and an underlayer disposed between the substrate and the magnetic layer. The underlayer is made of an ordered intermetallic material of FCC L1 2  or FCT L1 0  crystalline structure, so that c-axis of the magnetic layer is aligned in a predetermined direction.

This application is a Continuation-In-Part application of a U.S. patentapplication Ser. No. 09/584,603 filed May 31, 2000.

This application claims the benefit of Japanese Patent ApplicationsNo.11-322961 filed Nov. 12, 1999 and No.2001-109006 filed Apr. 6, 2001,in the Japanese Patent Office, the disclosures of which are herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to magnetic recording media andmagnetic storage apparatuses, and more particularly to a magneticrecording medium and a magnetic storage apparatus which are suited forhigh-density longitudinal magnetic recording.

2. Description of the Related Art

The recording density of longitudinal magnetic recording media, such asmagnetic disks, has been increased considerably, due to the reduction ofmedium noise and the development of magnetoresistive andhigh-sensitivity spin-valve heads. A typical longitudinal magneticrecording medium is comprised of a substrate, a seed layer, anunderlayer, a magnetic layer where information is written, a C or aDiamond-Like C (DLC) overlayer, and an organic lubricant layer which aresuccessively stacked in this order. For example, the underlayer is madeof Cr or a Cr-based alloy, and the magnetic layer is made of aCoCr-based alloy.

The medium noise is reduced by decreasing the exchange coupling betweengrains, by promoting more Cr segregation in the CoCr-based alloy whichforms the magnetic layer. Lowering the medium noise also involvesdecreasing the grain size and grain size distribution of the magneticlayer, for example, by reducing the thickness of the underlayer.Underlayers which are made of materials such as CrMo, CrTiB, NiAl or thelike are presently used in longitudinal magnetic recording media.

The underlayer described above also promotes crystallographic axis(c-axis or magnetic anisotropy axis) orientation in a plane whichincreases remanence magnetization and thermal stability of bits on themagnetic layer. Much success has been realized with an underlayer havinga B2 crystal structure, such as NiAl and FeAl which have the (211)texture when deposited on a glass substrate.

However, the (211) texture is weak for the underlayer having the B2crystal structure, including NiAl and FeAl. For this reason, it isnecessary to increase the thickness of the underlayer in order toimprove the (211) texture and to obtain a sufficiently high mediumcoercivity, as compared to a case where a Cr-based alloy is formed on aNiP layer. As a result, there are limitations in controlling the grainsize and the grain size distribution of the magnetic layer by way ofreducing the thickness of the underlayer, and that it is difficult tofurther improve the signal-to-noise ratio (SNR) of the longitudinalmagnetic recording medium.

On the other hand, perpendicular magnetic recording media holds promisefor high-density recording due to thermal stability of high-densitybits. Compared to longitudinal magnetic recording media, theperpendicular magnetic recording media have favorable demagnetizingfields for high linear densities.

A typical perpendicular magnetic recording medium includes a substratewhich is usually made of a glass ceramic, a seed layer made of CoCr orTi, and a magnetic layer made of a Co-based alloy where information iswritten, an overlayer made of C or Diamond-Like C (DLC), and an organiclubricant layer on the overlayer.

Another typical perpendicular magnetic recording medium has a doublemagnetic layer structure made up of a soft magnetic layer under theCo-based magnetic layer. The soft magnetic layer is usually made of aNiFe or FeSiAl.

As in the case of the longitudinal magnetic recording medium, the mediumnoise of the perpendicular magnetic recording medium is reduced bydecreasing the exchange coupling between grains, by promoting more Crsegregation in a Co-based alloy which forms the magnetic layer. Loweringthe medium noise also involves reducing the grain size and grain sizedistribution of the magnetic layer, and the proper use of the seed layerwhich is made of the material such as CoCr and Ti to promote a (0002)growth for the magnetic layer.

However, the conventional perpendicular magnetic recording media do nothave a means of controlling or considerably reducing the grain size andgrain size distribution of the magnetic layer, and there is a problem inthat it is difficult to greatly improve the medium signal-to-noise ratio(SNR).

SUMMARY OF THE INVENTION

Accordingly, it is a general object of the present invention to providea novel and useful magnetic recording medium and magnetic storageapparatus, in which the problems described above are eliminated.

Another and more specific object of the present invention is to providea magnetic recording medium comprising a substrate, a magnetic layermade of a Co or Co-based alloy, and an underlayer disposed between thesubstrate and the magnetic layer, where the underlayer is made of anordered intermetallic material of FCC L1₂ or FCT L1₀ crystallinestructure, so that c-axis of the magnetic layer is aligned in apredetermined direction. According to the magnetic recording medium ofthe present invention, it is possible to simultaneously improve thetexture of the underlayer and control the grain size and the grain sizedistribution of the magnetic layer, to thereby enable furtherimprovement of the SNR of the magnetic recording medium. Thepredetermined direction may be substantially parallel to orsubstantially perpendicular to an in-plane direction of the magneticlayer, so as to obtain a longitudinal magnetic recording medium or aperpendicular magnetic recording medium.

Still another object of the present invention is to provide a method ofproducing a magnetic recording medium which includes a base layer, amagnetic layer made of Co or a Co-based alloy, and an underlayerdisposed between the base layer and the magnetic layer, comprising thestep of depositing the underlayer which is made of a (111)-texturedordered intermetallic material of FCC L1₂ crystalline structure or FCTL1₀ crystalline structure on the base layer which is made of glass oroxidized NiP, at a deposition temperature of approximately 140 toapproximately 180° C. According to the method of producing the magneticrecording medium of the present invention, it is possible tosimultaneously improve the texture of the underlayer and control thegrain size and the grain size distribution of the magnetic layer, tothereby enable further improvement of the SNR of the magnetic recordingmedium.

A further object of the present invention is to provide a magneticstorage apparatus comprising a head, and at least one magnetic recordingmedium which includes a substrate, a magnetic layer made of Co or aCo-based alloy, and an underlayer disposed between the substrate and themagnetic layer, where the underlayer is made of an ordered intermetallicmaterial of FCC L1₂ crystalline structure or FCT L1₀ crystallinestructure on the substrate, so that c-axis of the magnetic layer isaligned in a predetermined direction. According to the magnetic storageapparatus of the present invention, it is possible to simultaneouslyimprove the texture of the underlayer and control the grain size and thegrain size distribution of the magnetic layer, to thereby enable furtherimprovement of the SNR of the magnetic recording medium, so that ahigh-quality high-density recording and reproduction can be achieved. Inaddition, the predetermined direction may be substantially parallel toor substantially perpendicular to an in-plane direction of the magneticlayer, so as to realize a longitudinal magnetic recording andreproduction or a perpendicular magnetic recording and reproduction.

Other objects and further features of the present invention will beapparent from the following detailed description when read inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE INVENTION

FIG. 1 is a cross sectional view showing an important part of a firstembodiment of a magnetic recording medium according to the presentinvention;

FIG. 2 is a diagram showing an ordered FCC L1₂ crystalline structurewhich may be used for the underlayer;

FIG. 3 is a diagram showing the lattice parameters a and the % mismatchfrom 4.1 Å, for various Al-based alloys having the L1₂ crystallinestructure;

FIG. 4 is a diagram showing an ordered FCT L1₀ crystalline structurewhich may be used for the underlayer;

FIG. 5 is a diagram showing a BCC crystal structure of a Cr underlayerwith the lattice parameter a of 2.884 Å;

FIG. 6 is a diagram showing a B2 crystal structure of a NiAl or FeAlunderlayer the lattice parameter a of 2.887 Å;

FIG. 7 is a cross sectional view showing an important part of a secondembodiment of the magnetic recording medium according to the presentinvention;

FIG. 8 is a cross sectional view showing an important part of a thirdembodiment of the magnetic recording medium according to the presentinvention;

FIG. 9 is a cross sectional view showing an important part of a fourthembodiment of the magnetic recording medium according to the presentinvention;

FIG. 10 is a cross sectional view showing an important part of a firstembodiment of a magnetic storage apparatus according to the presentinvention;

FIG. 11 is a plan view showing the important part of the firstembodiment of the magnetic storage apparatus;

FIG. 12 is a cross sectional view showing an important part of a fifthembodiment of the magnetic recording medium according to the presentinvention;

FIG. 13 is a cross sectional view showing an important part of a sixthembodiment of the magnetic recording medium according to the presentinvention;

FIGS. 14A through 14D respectively are diagrams showing a XRD spectrumof an underlayer and a magnetic layer for different underlayerthicknesses and deposition temperatures; and

FIGS. 15A through 15D respectively are diagrams showing Kerrmagnetization loops for a Co-based alloy on a TiAl-based alloy ground onglass at different deposition temperatures.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of a magnetic recording medium according to the presentinvention, a magnetic storage apparatus according to the presentinvention and a method of producing a magnetic recording mediumaccording to the present invention, will now be described with referenceto the accompanying drawings.

FIG. 1 is a cross sectional view showing an important part of a firstembodiment of a magnetic recording medium according to the presentinvention. In this embodiment, the present invention is applied to alongitudinal magnetic recording medium.

The magnetic recording medium shown in FIG. 1 includes a substrate 1made of Al or glass ceramic, a NiP layer 2, a seed layer 3, anunderlayer 4, an intermediate layer 5 made of a Cr-based alloy, aCoCr-based alloy layer 6, a magnetic layer 7 made of Co or a Co-basedalloy such as a CoCr-based alloy, a C or DLC overlayer 8, and an organiclubricant layer 9 which are successively stacked in the order shown.

The NiP layer 2 is preferably oxidized and/or mechanically textured.When oxidized, NiP forms a good base for the growth of Cr (002) texture.NiP is hard and is essential for tribology purposes. The NiP can also betextured which improves the medium orientation ratio while reducing headslider stiction.

The seed layer 3 is provided to promote adhesion and/or crystallographictexture of the underlayer 4 formed thereon. The seed layer 3 is made ofa Cr-based alloy including a material selected from a group of Mo, Ti, Vand W. Cr-rich alloys with the BCC crystal structure tend to grow a(002) texture on oxidized NiP. Hence, the provision of the Cr-rich seedlayer 3 promotes an in-plane orientation (1120) for the magnetic layer 7which is made of the CoCr-based alloy, for example.

The underlayer 4 is comprised of an ordered intermetallic material ofFace-Centered Cubic (FCC) L1₂ or Face-Centered-Tetragonal (FCT) L1₀crystalline structure, with a thickness of 3 to 100 nm, so as to promoteformation of small grain sizes and reduced grain size distribution inthe magnetic layer 7.

The underlayer 4 comprised of the L1₂ crystalline structure material maybe Al₅CuZr₂, Al₅CuHf₂, (AlCr)₃Ti, Al₆₇Cr₈Ti₂₅, Al₅NiZr₂, Al₅CuTi₂,Al₅NiNb₂, Al₃₀Dy₇Hf₃, Al₃₀Dy₇Zr₃, Al₃Er, Al₁₅HfHo₄, and Al₆₀Hf₇Tb₁₃.Such materials used for the underlayer 4 have the proper crystalstructure and lattice parameter to promote epitaxy with the magneticlayer 7, since Co c-parameter is 0.406 nm.

On the other hand, the underlayer 4 comprised of the L1₀ crystallinestructure may be γ-TiAl. This material γ-TiAl used for the underlayer 4has the proper crystal structure and lattice parameter to promoteepitaxy with the magnetic layer 7. Because γ-TiAl is FCT, this materialgrows a (001) texture which enhances the c-axis of the magnetic layer 7to be in-plane. In this case, the underlayer 4 may be made slightlyAlrich so that the Al content is 51 to 55 at. %. The presence of toomuch twinning may reduce the magnetic coercivity of the magnetic layer7. However, this slightly Al-rich composition range of the underlayer 4reduces twinning which is very common for FCC materials.

In either case where the underlayer 4 is comprised of the L1₂ or L1₀crystalline structure, the underlayer 4 may be alloyed with at least oneelement selected from a group of B, Cr, Hf, Mo, Mn, Ta, Ti, V, Zr oralloys thereof. In this case, it becomes possible to promote smallergrain sizes and to reduce stress due to better lattice matching in themagnetic layer 7 by the alloying of such elements.

Furthermore, the underlayer 4 may be made essentially of tetragonalAl₃Ti which is alloyed with an element selected from a group of Ni, Cu,Cr, Mn, Zn, Fe, Co, Ag, Pd, Pt, Au and Rh which make the L1₀ crystallinestructure into the L1₂ crystalline structure. Alloying the tetragonalAl₃Ti with the above elements transforms the L1₀ crystalline structureinto the L1₂ crystalline structure, which makes the crystallographicplanes such as (100), (010) and (001) have similar dimensions whichprovide a more uniform lattice for the magnetic layer 7 to grow on orfor the intermediate layer 5 to grow on.

In this embodiment, the underlayer 4 has a lattice parameter a whichsatisfies 3.9 Å≦a≦4.3 Å. This range of the lattice parameter a matchesthat of the magnetic layer 7, to better promote epitaxy.

The intermediate layer 5 is made of a Cr-M alloy having a BCC crystalstructure with a thickness of 1 to 30 nm, where M is an element selectedfrom a group of B, Mn, Mo, Ti, V and W. Such materials used for theintermediate layer 5 has the proper lattice parameter to promote epitaxywith the magnetic layer 7. In addition, Cr adheres very well to variouskinds of materials such that the Cr-M alloy makes a good buffer layerbetween the underlayer 4 and the magnetic layer 7.

The CoCr-based alloy layer 6 has a HCP crystal structure with athickness of 1 to 10 nm, and is used to promote epitaxy and to narrowthe grain size distribution of the magnetic layer 7. When a CoCr-basedalloy magnetic layer having the HCP crystal structure is grown directlyon a Cr-based layer having the BCC crystal structure, a portion of themagnetic layer in contact with this Cr-based layer having the BCCcrystal structure is adversely affected due to the lattice mismatchand/or Cr diffusion. In this case, the magnetic anisotropy as well asthe total magnetization of the magnetic layer are reduced. On the otherhand, the use of the non-magnetic CoCr-based alloy layer 6 having theHCP crystal structure prevents such undesirable effects on the magneticlayer 7. As a result, this embodiment can increase the magneticanisotropy and the coercivity of the magnetic layer 7, and also improvethe in-plane orientation. The full magnetization of the magnetic layer 7is also obtainable and the so-called “dead layer” portion is minimized.Moreover, the formation of smaller grains at the interface portion ofthe magnetic layer 7 is reduced.

The magnetic layer 7 may be made of a CoCrPt—X alloy with a thickness of5 to 30 nm, where X is an element selected from a group of B, Cu, Mo,Ta, W and alloys thereof.

The C or DLC overlayer 8 protects the magnetic recording medium when incontact with a head. This overlayer 8 also protects the magnetic layer 7from corrosion.

FIG. 2 shows an ordered FCC L1₂ crystalline structure which may be usedfor the underlayer 4. For example, the crystalline structure shown inFIG. 2 belongs to Cu₃Au as well as many other alloys. However, in orderfor the lattice parameter of the underlayer 4 to substantially matchthat of a Cr or Cr-based magnetic layer having the HCP crystalstructure, the lattice parameter of the underlayer 4 has to beapproximately 4.1 Å.

Most materials having the L1₂ crystalline structure with the properlattice parameter that will substantially match that of the Cr orCr-based magnetic layer having the HCP crystal structure are Al-basedalloys, as shown in FIG. 3. FIG. 3 shows the lattice parameters a andthe % mismatch from 4.1 Å, for various Al-based alloys having the L1₂crystalline structure. The various Al-based alloys having the L1₂crystalline structure include Al₅CuHf₂, Al₅CuTi₂, Al₅CuZr₂, Al₃₀Dy₇Hf₃,Al₃₀Dy₇Zr₃, Al₃Er, Al₁₅HfHo₄, Al₆₀Hf₇Tb₁₃, Al₅NiNb₂, and Al₅NiZr₂.

On the other hand, FIG. 4 shows an ordered FCT L1₀ crystalline structurewhich may be used for the underlayer 4. For example, the crystallinestructure shown in FIG. 4 belongs to γ-TiAl. Although γ-TiAl istetragonal, the lattice parameters a and c are a=0.4005 nm and c=0.407nm which are not very different from those of the magnetic layer 7, anda ratio a/c is close to 1. Hence, it may be seen that γ-TiAl is suitedfor use as the underlayer 4. Doping γ-TiAl with other elements affectsthe electronic structure which reduces tegragonality.

For comparison purposes, FIGS. 5 and 6 respectively show a BCC crystalstructure of a Cr underlayer with the lattice parameter a of 2.884 Å,and a B2 crystal structure of a NiAl or FeAl underlayer the latticeparameter a of 2.887 Å.

With regard to FIG. 5, the Cr[110] lattice spacing of 4.08 Å matchesCo-based magnetic layers such as CoCrPt-M alloys, where M is Ta, Ni, Wor B (d(0002)˜4.1 Å). Cr is usually alloyed with V, W or Mo to expandthe lattice parameter to better match the increasing lattice parametersof Co-based alloys with higher Pt content, for example.

With regard to FIG. 6, NiAl has lattice parameter a which is very closeto that of Cr and makes an appropriate underlayer for Co-based magneticlayers having the HCP crystal structure, such as a CoCr-based alloy.NiAl is an ordered intermetallic alloy and tends to form smaller grainswhen sputter deposited as compared to Cr-based alloys. As a result, NiAlpromotes small grain sizes and good grain size distribution for magneticlayers deposited thereon. NiAl grows with a (211) and (110) textureswhich promote Co(10{overscore (1)}0) resulting in the c-axis of themagnetic layer becoming in-plane. However, the (211) texture is weak,and the presence of the (110) texture results in anisotropy orientationslargely out of the plane as compared to Cr(002) which reveals excellentin-plane c-axis orientation. Moreover, NiAl need to be relatively thickin order to obtain a proper coercivity for the magnetic layer.

Therefore, it may be seen that using a Cr underlayer or a NiAl underlayer cannot simultaneously achieve (i) excellent in-plane c-axisorientation and (ii) reduced grain size of the magnetic layer, unlikethe first embodiment described above.

Next, a description will be given of a second embodiment of the magneticrecording medium according to the present invention, by referring toFIG. 7. FIG. 7 is a cross sectional view showing an important part ofthe second embodiment of the magnetic recording medium. In FIG. 7, thoseparts which are the same as those corresponding parts in FIG. 1 aredesignated by the same reference numerals, and a description thereofwill be omitted. In this embodiment, the present invention is applied toa longitudinal magnetic recording medium.

In FIG. 7, the underlayer 4 has a multi-layer structure. For the sake ofconvenience, FIG. 7 shows a case where the underlayer 4 has a bi-layerstructure, including a first layer 4 a and a second layer 4 b. Each ofthe first and second layers 4 a and 4 b is comprised of an orderedintermetallic material of FCC L1₂ or FCT L1₀ crystalline structure, andthe same materials used for the underlayer 4 in the first embodiment,including the materials shown in FIG. 3, may be used for each of thefirst and second layers 4 a and 4 b.

Some L1₂ or L1₀ crystalline structures are better suited for controllinggrain sizes and texture, while others may show improvement withthickness but do not grow the proper crystallographic texture whendirectly grown on a particular surface material. Accordingly, the use ofthe underlayer 4 having the multi-layer structure can more positivelyand simultaneously achieve excellent in-plane c-axis orientation andreduced grain size of the magnetic layer 7.

Next, a description will be given of a third embodiment of the magneticrecording medium according to the present invention, by referring toFIG. 8. FIG. 8 is a cross sectional view showing an important part ofthe third embodiment of the magnetic recording medium. In FIG. 8, thoseparts which are the same as those corresponding parts in FIG. 1 aredesignated by the same reference numerals, and a description thereofwill be omitted. In this embodiment, the present invention is applied toa longitudinal magnetic recording medium.

In this embodiment, the substrate 1 is made of glass, and a seed layer 3is formed directly on the substrate 1. This seed layer 3 is made of NiAlor FeAl having a B2 crystal structure. NiAl and FeAl having the B2crystal structure tend to grow a (211) texture on glass. Accordingly,this embodiment can promote the in-plane orientation (10{overscore(1)}0) for the CoCr-based magnetic layer 7 which has less stress thanthat with Cr-based underlayers due to lattice matching. Hence, thisembodiment is suited for a case where a Co(10{overscore (1)}0)orientation is favoured on the glass substrate 1.

Next, a description will be given of a fourth embodiment of the magneticrecording medium according to the present invention, by referring toFIG. 9. FIG. 9 is a cross sectional view showing an important part ofthe fourth embodiment of the magnetic recording medium. In FIG. 9, thoseparts which are the same as those corresponding parts in FIG. 7 aredesignated by the same reference numerals, and a description thereofwill be omitted. In this embodiment, the present invention is applied toa longitudinal magnetic recording medium.

In this embodiment, the underlayer 4 of the third embodiment has thebi-layer structure of the second embodiment. In other words, theunderlayer 4 is made up of the first and second layers 4 a and 4 b.

Next, a description will be given of a modification which is applicableto any of the first through fourth embodiments described above.

In this modification, the seed layer 3, which is disposed between thesubstrate 1 and the magnetic layer 7, is made of an orderedintermetallic material of FCC L1₂ or FCT L1₀ crystalline structure. Inaddition, the underlayer 4 is made of Cr-M, NiAl or FeAl, where M is anelement selected from a group of B, Mn, Mo, Ti, V and W. Further, aferromagnetic material selected from a group of CoCrTa, CoCrPt, CoCrPtB,CoCrPtTa, CoCrPtTaB, CoCrPtTaNb and CoCrPtWB and having a thickness of 5to 30 nm may be used for the magnetic layer 7.

Next, a description will be given of a first embodiment of a magneticstorage apparatus according to the present invention, by referring toFIGS. 10 and 11. FIG. 10 is a cross sectional view showing an importantpart of this first embodiment of the magnetic storage apparatus, andFIG. 11 is a plan view showing the important part of this firstembodiment of the magnetic storage apparatus.

As shown in FIGS. 10 and 11, the magnetic storage apparatus generallyincludes a housing 13. A motor 14, a hub 15, a plurality of magneticrecording media 16, a plurality of recording and reproducing (read andwrite) heads 17, a plurality of suspensions 18, a plurality of arms 19,and an actuator unit 20 are provided within the housing 13. The magneticrecording media 16 are mounted on the hub 15 which is rotated by themotor 14. The recording and reproducing head 17 is made up of areproducing head such as a MR or GMR head, and a recording head such asan inductive head. Each recording and reproducing head 17 is mounted onthe tip end of a corresponding arm 19 via the suspension 18. The arms 19are moved by the actuator unit 20. The basic construction of thismagnetic storage apparatus is known, and a detailed description thereofwill be omitted in this specification.

This embodiment of the magnetic storage apparatus is characterized bythe magnetic recording media 16. Each magnetic recording medium 16 hasthe structure of any of the first through fourth embodiments of themagnetic recording medium described above in conjunction with FIGS. 1through 9, or the modification thereof. Of course, the number ofmagnetic recording media 16 is not limited to three, and only one, twoor four or more magnetic recording media 16 may be provided.

The basic construction of the magnetic storage apparatus is not limitedto that shown in FIGS. 10 and 11. In addition, the longitudinal magneticrecording medium used in the present invention is not limited to amagnetic disk.

FIG. 12 is a cross sectional view showing an important part of a fifthembodiment of the magnetic recording medium according to the presentinvention. In this fifth embodiment, the present invention is applied toa perpendicular magnetic recording medium. This fifth embodiment of themagnetic recording medium is produced by a first embodiment of themethod of producing the magnetic recording medium according to thepresent invention.

The magnetic recording medium shown in FIG. 12 includes a substrate 51made of Al, a glass ceramic or the like, a seed layer 52 made of NiP orthe like, an underlayer 53 made of a (111)-textured orderedintermetallic material of Face-Centered Cubic (FCC) L1₂ crystallinestructure or Face-Centered-Tegragonal (FCT) L1₀ crystalline structure,an adhesive layer 54 made of a Cr-based alloy or the like, anintermediate layer 55 made of a CoCr-based alloy or the like having aHCP crystal structure, a magnetic layer 56 made of Co or a Co-basedalloy, a protective layer 57 made of C, DLC or the like, and a lubricantlayer 58 made of an organic lubricant or the like.

The NiP seed layer 52 may be oxidized by exposure to air or by in situO₂ gas introduction into a sputtering chamber before deposition of theunderlayer 53. On the other hand, for some substrates it is notessential to provide the seed layer 52, and the seed layer 52 may beomitted.

The underlayer 53 is made of the (111)-textured FCC L1₂ crystallinestructure or the FCT L1₀ crystalline structure, so as to promoteformation of small grain sizes and reduced grain size distribution inthe magnetic layer 56. The underlayer 53 is preferably deposited aboveroom temperature and less than approximately 240° C. to a thickness ofapproximately 1 to approximately 15 nm, for example. An optimumdeposition temperature may differ depending on the substrate material.For a TiAl-on-glass substrate, good results were obtained for adeposition temperature Ts of approximately 140 to approximately 180° C.,and preferably approximately 160° C. Intermetallic grains of theunderlayer 53 are expected to be small due to the large chemical bindingenergies.

The underlayer 53 comprised of the L1₂ crystalline structure materialmay be Al₅CuZr₂, Al₅CuHf₂, (AlCr)₃Ti, Al₆₇Cr₈Ti₂₅, Al₅NiZr₂, Al₅CuTi₂,Al₅NiNb₂, Al₃₀Dy₇Hf₃, Al₃₀Dy₇Zr₃, Al₃Er, Al₁₅HfHo₄, and Al₆₀Hf₇Tb₁₃.Such materials used for the underlayer 53 have the proper crystalstructure and lattice parameter to promote epitaxy with the magneticlayer 56, since a lattice parameter c of Co is c=0.406 nm.

On the other hand, the underlayer 53 comprised of the L1₀ crystallinestructure may be γ-TiAl. This material γ-TiAl used for the underlayer 53has the proper crystal structure and lattice parameter to promoteepitaxy with the magnetic layer 56. Though γ-TiAl is FCT, the a/c ratiois close to 1 and this material grows a (111) texture which enhances thec-axis of the magnetic layer 56 to be substantially normal(perpendicular) to an in-plane direction (a film plane) of the magneticlayer 56. In this case, the underlayer 53 may be made slightly Al-richso that the Al content is 51 to 55 at. %. The presence of too muchtwinning may reduce the magnetic coercivity of the magnetic layer 56.However, this slightly Al-rich composition range of the underlayer 53reduces twinning which is very common for FCC materials.

In either case where the underlayer 53 is comprised of the L1₂ or L1₀crystalline structure, the underlayer 53 may be alloyed with at leastone element selected from a group of B, Cr, Hf, Mo, Mn, Ta, Ti, V, Zr oralloys thereof. In this case, it becomes possible to promote smallergrain sizes and to reduce stress due to better lattice matching in themagnetic layer 56 by the alloying of such elements.

Furthermore, the underlayer 53 may be made essentially of tetragonalAl₃Ti which is alloyed with an element selected from a group of Ni, Cu,Cr, Mn, Zn, Fe, Co, Ag, Pd, Pt, Au and Rh which make the L1₀ crystallinestructure into the L1₂ crystalline structure. Alloying the tetragonalAl₃Ti with the above elements transforms the L1₀ crystalline structureinto the L1₂ crystalline structure, which makes the crystallographicplanes such as (100), (010) and (001) have similar dimensions whichprovide a more uniform lattice for the magnetic layer 56 to grow on orfor the adhesive layer 54 to grow on.

In this embodiment, the underlayer 53 has a lattice parameter a whichsatisfies 3.9 Å≦a≦4.3 Å. This range of the lattice parameter a matchesthat of the magnetic layer 56, to better promote epitaxy, and the c-axisof the magnetic layer 56 becomes substantially normal (perpendicular) tothe in-plane direction of the magnetic layer 56. Further, the underlayer53 preferably has a thickness in a range of approximately 10 to 40 nm.

The adhesive layer 54 improves the magnetic layer anisotropy of themagnetic layer 56, by improving the adhesion between the underlayer 53and the magnetic layer 56. The adhesive layer 54 is made of a Cr-M alloyhaving a BCC crystal structure with a thickness of approximately 1 toapproximately 15 nm, where M is an element selected from a group of B,Fe, Mn, Mo, Ti, V and W. Such materials used for the adhesive layer 55has the proper lattice parameter to promote epitaxy with the magneticlayer 56. In addition, Cr adheres very well to various kinds ofmaterials such that the Cr-M alloy makes a good buffer layer between theunderlayer 53 and the magnetic layer 56.

The intermediate layer 55 made of the CoCr-based alloy having the HCPcrystal structure is formed to a thickness of approximately 1 toapproximately 15 nm, and is used to promote epitaxy and to narrow thegrain size distribution of the magnetic layer 56. When a CoCr-basedmagnetic layer having a HCP crystal structure is grown directly on aCr-based layer having the BCC crystal structure, a portion of themagnetic layer in contact with this Cr-based layer having the BCCcrystal structure is adversely affected due to the lattice mismatchand/or Cr diffusion. In this case, the magnetic anisotropy as well asthe total magnetization of the magnetic layer are reduced. On the otherhand, the use of the non-magnetic CoCr-based alloy having the HCPcrystal structure for the intermediate layer 55 prevents suchundesirable effects on the magnetic layer 56. As a result, it ispossible to increase the magnetic anisotropy and the coercivity of themagnetic layer 56, and also improve the orientation substantially normal(perpendicular) to the in-plane direction of the magnetic layer 56. Thefull magnetization of the magnetic layer 56 is also obtainable and theso-called “dead layer” portion is minimized. Moreover, the formation ofsmaller grains at the interface portion of the magnetic layer 56 isreduced.

The magnetic layer 56 may be made of Co or a Co-based alloy whichincludes a CoCrPt—X alloy, with a thickness of approximately 5 toapproximately 30 nm, where X is an element selected from a group of B,Cu, Mo, Ta, W and alloys thereof. The magnetic layer 56 is preferablydeposited at a temperature of approximately 200° C. to enhance Crsegregation. A two-step heating process may be employed to optimize the(111) texture of the underlayer 53 and the Cr segregation in themagnetic layer 56. The Co (0002) texture of the magnetic layer 56 ispromoted by the (111) texture of the underlayer 53.

The C or DLC overlayer 57 protects the magnetic recording medium when incontact with a head. This overlayer 57 also protects the magnetic layer56 from corrosion.

An ordered FCC L1₂ crystalline structure which may be used for theunderlayer 53 is the same as the crystalline structure shown in FIG. 2described above. However, in order for the lattice parameter of theunderlayer 54 to substantially match that of a Cr or Cr-based magneticlayer having the HCP crystal structure, the lattice parameter of theunderlayer 54 has to be approximately 4.1 Å.

Most materials having the L1₂ crystalline structure with the properlattice parameter that will substantially match that of the Cr orCr-based magnetic layer having the HCP crystal structure are Al-basedalloys, as shown in FIG. 3.

On the other hand, an ordered FCT L1₀ crystalline structure which may beused for the underlayer 53 is the same as the crystalline structureshown in FIG. 4 described above. For example, the crystalline structureshown in FIG. 4 belongs to γ-TiAl which is tetragonal, but the latticeparameters a and c are a=0.4005 nm and c=0.407 nm which are not verydifferent from those of the magnetic layer 56, and the ratio a/c isclose to 1. Hence, it may be seen that γ-TiAl is suited for use as theunderlayer 53. Doping γ-TiAl with other elements affects the electronicstructure which reduces tetragonality.

FIG. 13 is a cross sectional view showing an important part of a sixthembodiment of the magnetic recording medium according to the presentinvention. In this sixth embodiment, the present invention is applied toa perpendicular magnetic recording medium. In FIG. 13, those parts whichare the same as those corresponding parts in FIG. 12 are designated bythe same reference numerals, and a description thereof will be omitted.This sixth embodiment of the magnetic recording medium is produced by asecond embodiment of the method of producing the magnetic recordingmedium according to the present invention.

The magnetic recording medium shown in FIG. 13 includes an adhesivelayer 60 on the substrate 51, a soft magnetic layer 61 on the adhesivelayer 60, and a seed layer 62 on the soft magnetic layer 61. Theunderlayer 53 is provided on the seed layer 62. In other words, in thisembodiment, the present invention is applied to the perpendicularmagnetic recording medium having the double magnetic layer structure.The underlayer 53 preferably has a thickness in a range of approximately5 to 10 nm.

The adhesive layer 60 is made of a Cr-based alloy or the like, and isdeposited to a thickness of approximately 1 to approximately 5 nm.

The soft magnetic layer 61 is made of an amorphous or nanocrystallinesoft magnetic material, and is deposited to a thickness of approximately100 nm or greater. The amorphous or nanocrystalline soft magneticmaterial promotes small grains of the seed layer 62 and consequently ofthe magnetic layer 56. The double magnetic layer structure enables theuse of a single-pole head and a high field compared to the singlemagnetic layer structure of the first embodiment with a ring head.However, the soft magnetic layer 61 becomes a medium noise source due toirregular magnetic domains formed therein. For this reason, it ispreferable to have the easy axis of magnetization of the soft magneticlayer 61 in a direction crossing the recording track direction, that is,to have the hard axis of magnetization of the soft magnetic layer 11parallel to the recording track direction, in order to minimize themedium noise.

The seed layer 62 is made of an amorphous or crystalline material, suchas NiP and Ta, which is deposited to a thickness of approximately 1 toapproximately 3 nm and subsequently oxidized. The use of the amorphousmaterial for the seed layer 62 promotes small grain sizes of theunderlayer 53, especially when the soft magnetic layer 61 is not made ofan amorphous material. In addition, when NiP or Ta is used for the seedlayer 62, an amorphous oxide layer can be formed on the surface of theseed layer 62 when the seed layer 62 is oxidized.

According to the fifth and sixth embodiments described above, it ispossible to promote more Cr segregation in a Co-based alloy which formsthe magnetic layer. Further, it is possible to reduce the medium noiseby reducing the grain size and grain size distribution of the magneticlayer, and by the use of the underlayer which is made of the(111)-textured ordered intermetallic material of FCC L1₂ crystallinestructure or FCT L1₀ crystalline structure which promotes a (0002)growth for the magnetic layer. Therefore, it is possible to greatlyimprove the medium SNR of the perpendicular magnetic recording medium.

Next, a description will be given of the results of experimentsconducted by the present inventors, confirming the improved performanceof the fifth and sixth embodiments described above, by referring toFIGS. 14A through 14D and FIGS. 15A through 15D. FIGS. 14A through 14Dare diagrams showing a XRD spectrum of the underlayer and a magneticlayer for different underlayer thicknesses and deposition temperatures.FIGS. 15A through 15D are diagrams showing Kerr magnetization loops fora Co-based alloy on a TiAl-based alloy ground on glass at differentdeposition temperatures.

FIG. 14A shows the XRD pattern for a 50 nm thick single TiAl layer andvarious perpendicular magnetic recording media having a multi-layerstructure CoCrPtTaB/Co₆₃Cr₃₇/Cr₉₀Mo₁₀/TiAl deposited at room temperatureon the glass substrate 51, where the CoCrPtTaB magnetic layer 56 has athickness of 23 nm, the Co₆₃Cr₃₇ intermediate layer 55 has a thicknessof 3 nm, the Cr₉₀Mo₁₀ adhesion layer 54 has a thickness of 10 nm, andthe TiAl underlayer 53 has a thickness t of t=20 to 80 nm in steps of 20nm. The 50 nm thick single TiAl layer revealed no diffraction peak,indicating that the grain sizes are either nanocrystalline or amorphous.Similar behavior was found for NiAl layers having an average graindiameter of approximately 9 to approximately 10 nm. On the other hand,of the multi-layer structures, the CoCrPtTaB magnetic layer 56 developed(1010), (1120) and (0002) textures for t=20 nm. The (1010) and (1120)textures are for making the c-axis of the CoCrPtTaB magnetic layer 56in-plane, while the (0002) texture is for making the c-axis of theCoCrPtTaB magnetic layer 56 substantially normal (perpendicular) to thein-plane direction. It may be regarded that the latter (0002) texture(2θ˜43°) is due to the (110) texture of the Cr₉₀Mo₁₀ adhesion layer 54.A slight (002) texture of the Cr₉₀Mo₁₀ adhesion layer 54 was alsoobserved indicating that the Cr₉₀Mo₁₀ adhesion layer 54 is notamorphous. As the thickness of the TiAl underlayer 53 increased, the(1010) and (0002) textures improved.

FIG. 14B shows the XRD pattern for the various perpendicular magneticrecording media having the above multi-layer structureCoCrPtTaB/Co₆₃Cr₃₇/Cr₉₀Mo₁₀/TiAl deposited at the temperature Ts of 160°C. on the glass substrate 51. The TiAl underlayer 53 has the thickness tof t=20 nm and t=40 nm. The TiAl underlayer 53 revealed a very intense(111) texture even at the thickness t of t=20 nm, which leads to anintense peak at the (0002) texture of the CoCrPtTaB magnetic layer 56. ACo (1011) texture also developed, but was dominated by the peak at the(0002) texture.

FIG. 14C shows the XRD pattern for the various perpendicular magneticrecording media having the above multi-layer structureCoCrPtTaB/Co₆₃Cr₃₇/Cr₉₀Mo₁₀/TiAl deposited at the temperature Ts of 200°C. on the glass substrate 51. The TiAl underlayer 53 has the thickness tof t=20 to 60 nm in steps of 20 nm. In addition, a case where noCoCrPtTaB magnetic layer 56 is provided and a case where no Cr₉₀Mo₁₀adhesion layer 54 is provided are also shown for t=60 nm. The peak ofthe (111) texture of the TiAl underlayer 53 and the Cr (111) textureappeared only at the thickness t of t=40 nm, but the Co (0002) texturewas already present. A further increase in the thickness t increased theintensity of the peaks of the (111) texture and the (0002) texture. Forthe thickness t of t=60 nm, a peak of the (1011) texture was lessintense when no Cr₉₀Mo₁₀ adhesion layer 54 was provided between the TiAlunderlayer 53 and the Co₆₃Cr₃₇ intermediate layer 55.

FIG. 14D shows the XRD pattern for the various perpendicular magneticrecording media having the above multi-layer structureCoCrPtTaB/Co₆₃Cr₃₇/Cr₉₀Mo₁₀/TiAl deposited at the temperature Ts of 240°C. on the glass substrate 51. The TiAl underlayer 53 has the thickness tof t=20 nm and t=40 nm. In this case, the increase of the temperature Tslead to a suppression of the peak of the (111) texture of the TiAl layer53 especially at small values for the thickness t. In addition, some ofthe c-axis of the CoCrPtTaB magnetic layer 56 was in-plane for t=20 to40 nm.

FIGS. 15A, 15B, 15C and 15D respectively show the Kerr magnetizationloops, that is, the perpendicular hysteresis loops, for the variousperpendicular magnetic recording media shown in FIGS. 14A, 14B, 14C and14D for the thickness t of t=20 nm of the TiAl underlayer 53. It wasconfirmed that the perpendicular magnetic recording medium shown in FIG.15B shows the largest coercivity in the direction normal (perpendicular)to the in-plane direction of the CoCrPtTaB magnetic layer 56.

Therefore, it was confirmed that the orientation of the magnetic layer56 is controllable by simply varying the thickness t and the depositiontemperature Ts of the underlayer 53. It was found desirable that thedeposition temperature Ts is approximately 140 to approximately 180° C.,and preferably approximately 160° C.

Next, a description will be given of a second embodiment of the magneticstorage apparatus according to the present invention. A cross sectionalview and a plan view of an important part of this second embodiment ofthe magnetic storage apparatus respectively are the same as the crosssectional view shown in FIG. 10 and the plan view shown in FIG. 11 ofthe first embodiment of the magnetic storage apparatus described above.

This second embodiment of the magnetic storage apparatus ischaracterized by the magnetic recording media 16. Each magneticrecording medium 16 has the structure of the fifth or sixth embodimentof the magnetic recording medium described above in conjunction withFIGS. 12 through 15D. Of course, the number of magnetic recording media16 is not limited to three, and only one, two or four or more magneticrecording media 16 may be provided.

The basic construction of the magnetic storage apparatus is not limitedto that shown in FIGS. 10 and 11. In addition, the perpendicularmagnetic recording medium used in the present invention is not limitedto a magnetic disk.

Further, the present invention is not limited to these embodiments, butvarious variations and modifications may be made without departing fromthe scope of the present invention.

What is claimed is:
 1. A magnetic recording medium comprising: asubstrate; a magnetic layer made of a Co or Co-based alloy; and anunderlayer disposed between said substrate and said magnetic layer,wherein said underlayer has a multi-layer structure, and each layer ofthe multi-layer structure is made of an ordered intermetallic materialof FCC L1₂ or FCT L1₀ crystalline structure, so that c-axis of saidmagnetic layer is aligned in a predetermined direction.
 2. The magneticrecording medium as claimed in claim 1, wherein said underlayer havingthe FCC L1₂ crystalline structure is selected from the group ofAl₅CuZr₂, Al₅CuHf₂, (AlCr)₃Ti, Al₆₇Cr₈Ti₂₅, Al₅NiZr₂, Al₅CuTi₂,Al₅NiNb₂, Al₃₀Dy₇Hf₃, Al₃₀Dy₇Zr₃, Al₃Er, Al₁₅HfHo₄, and Al₆₀Hf₇Th₁₃. 3.The magnetic recording medium as claimed in claim 1, wherein saidunderlayer having the FCT L1₀ crystalline structure is γ-TiAl.
 4. Themagnetic recording medium as claimed in claim 1, wherein said underlayeris alloyed with at least one element selected from the group of B, Cr,Hf, Mo, Mn, Ta, Ti, V, Zr or alloys thereof.
 5. The magnetic recordingmedium as claimed in claim 1, wherein said underlayer includestetragonal Al₃Ti which is alloyed with an element selected from thegroup of Ni, Cu, Cr, Mn, Zn, Fe, Co, Ag, Pd, Pt, Au and Rh which makethe FCT L1₀ crystalline structure into FCC L1₂ crystalline structure. 6.The magnetic recording medium as claimed in claim 1, wherein saidunderlayer has a lattice parameter a which satisfies 3.9 Å≦a≦4.3 Å. 7.The magnetic recording medium as claimed in claim 1, wherein saidpredetermined direction is substantially parallel to an in-planedirection of said magnetic layer.
 8. The magnetic recording medium asclaimed in claim 1, wherein said predetermined direction issubstantially perpendicular to an in-plane direction of said magneticlayer.
 9. The magnetic recording medium as claimed in claim 8, whereinsaid underlayer is made of a (111)-textured ordered intermetallicmaterial of FCC L1₂ or FCT L1₀ crystalline structure.
 10. The magneticrecording medium as claimed in claim 9, further comprising: a softmagnetic layer, made of an amorphous or nanocrystalline soft magneticmaterial, disposed between said substrate and said underlayer.
 11. Themagnetic recording medium as claimed in claim 10, wherein said softmagnetic layer has a hard axis of magnetization parallel to a recordingtrack direction.
 12. The magnetic recording medium as claimed in claim10, further comprising: a seed layer, made of an amorphous ornanocrystalline soft magnetic material, disposed between said softmagnetic layer and said underlayer.
 13. The magnetic recording medium asclaimed in claim 9, further comprising: an adhesive layer, made of aCr-M alloy having a BCC crystal structure, disposed between saidunderlayer and said magnetic layer, where M is an element selected froma group consisting of B, Fe, Mn, Mo, Ti, V and W.
 14. The magneticrecording medium as claimed in claim 13, further comprising: anintermediate layer, made of a CoCr-based alloy having a HCP crystalstructure, disposed between said adhesive layer and said magnetic layer.15. The magnetic recording medium as claimed in claim 9, furthercomprising: an intermediate layer, made of a CoCr-based alloy having aHCP crystal structure, disposed between said underlayer and saidmagnetic layer.
 16. A method of producing a magnetic recording mediumwhich includes a base layer, a magnetic layer made of Co or a Co-basedalloy, and a multilayered underlayer disposed between the base layer andthe magnetic layer, said method comprising step of: (a) depositing theunderlayer which is made of a (111)-textured ordered intermetallicmaterial of FCC L1₂ crystalline structure or FCT L1₀ crystallinestructure on the base layer which is made of glass or oxidized NiP, at adeposition temperature of approximately 140 to approximately 180° C. 17.The method of producing the magnetic recording medium as claimed inclaim 16, further comprising the step of: (b) depositing a soft magneticlayer made of an amorphous or nanocrystalline soft magnetic materialbetween the substrate and the underlayer.
 18. The method of producingthe magnetic recording medium as claimed in claim 17, further comprisingthe step of: (c) depositing a seed layer made of an amorphous ornanocrystalline soft magnetic material between the soft magnetic layerand the underlayer.
 19. The method of producing the magnetic recordingmedium as claimed in claim 16, further comprising the step of: (b)depositing an adhesive layer made of a Cr-M alloy having a BCC crystalstructure between the underlayer and the magnetic layer, where M is anelement selected from a group consisting of B, Fe, Mn, Mo, Ti, V and W.20. The method of producing the perpendicular magnetic recording mediumas claimed in claim 19, further comprising the step of: (c) depositingan intermediate layer made of a CoCr-based alloy having a HCP crystalstructure between the adhesive layer and the magnetic layer.
 21. Amagnetic storage apparatus comprising: a head; and at least one magneticrecording medium which includes a substrate, a magnetic layer made of Coor a Co-based alloy, and an underlayer disposed between the substrateand the magnetic layer, wherein said underlayer has a multi-layerstructure, and each layer of the multi-layer structure is made of anordered intermetallic material of FCC L1₂ or FCT L1₀ crystallinestructure, so that c-axis of the magnetic layer is aligned in apredetermined direction.
 22. The magnetic storage apparatus as claimedin claim 21, wherein said predetermined direction is substantiallyparallel to an in-plane direction of said magnetic layer.
 23. Themagnetic storage apparatus as claimed in claim 21, wherein saidpredetermined direction is substantially perpendicular to an in-planedirection of said magnetic layer.
 24. The magnetic storage apparatus asclaimed in claim 23, wherein said underlayer is made of a (111)-texturedordered intermetallic material of FCC L1₂ or FCT L1₀ crystallinestructure.